Over the past decade, much of the world's data has moved into the cloud. Projections indicate that by the beginning of the next decade, zettabytes of data will be stored in cloud-based storage. To meet the increasing demand, cloud providers rely on a variety of data-storage technologies. These include non-volatile memory (NVM), flash, hard disk drives (HDDs), magnetic tape, and optical discs. These storage technologies differ from each other in terms of cost, latency, throughput, storage density, failure rate, and media lifetime.
As one example, flash storage offers acceptable durability, high throughput, and low latency. A flash-provisioned service could be used, therefore, to handle current workloads in the cloud according to a single-storage type Service Level Agreement (SLA). However, the high cost of flash storage is prohibitive for very large volumes of data. On the cloud, therefore, this technology is used primarily to store so-called ‘hot’ data—i.e., recent or transient data. Cloud providers handle ‘cooler’ data using a segregated tier system, each tier having a different SLA, with pricing and performance characteristics dictated by the associated storage technology.